1. Field of the Invention
The present invention disclosed in the specification relates to a semiconductor device constituted by using a thin film transistor having a plurality of gate electrodes. Further, the present invention relates to a method of fabricating the semiconductor device.
2. Description of Related Art
In recent years, there has been increased thin film transistors using polycrystal silicon films in semiconductor layers. According to a thin film transistor using a polycrystal silicon film, high speed operation that is faster than operation of a thin film transistor using an amorphous silicon film by two digits or more can be performed since a mobility thereof is large.
Therefore, there poses a problem of hot carrier effect in which hot carriers generated in a channel jump into a gate insulating film and deteriorate a threshold voltage or a mutual conductance.
Conventionally, in respect of the above-described problem, there has been known a thin film transistor of a multi gate type alleviating the hot carrier effect by providing a plurality of gate electrodes and weakening an electric field applied on a single gate.
FIG. 5 shows an example where a thin film transistor of a conventional double gate type is used as a switching element of a pixel matrix portion of a liquid crystal display device.
As shown by FIG. 5, a semiconductor layer 02 and a source wiring 25 form a contact at a source electrode 22. Further, the semiconductor layer 02 is extended while meandering and intersects with a gate wiring 26 at regions 21 and 21'. Further, the semiconductor layer 02 and a pixel electrode 24 form a contact at a drain electrode 23. Portions of the gate wiring at the intersected regions 21 and 21' function as gate electrodes.
As is an apparent from FIG. 5, the conventional multi gate type thin film transistor is constituted by the gate wiring 26 in a substantially straight line shape and the meandering semiconductor layer 02.
By adopting such a constitution, a distance between the source and the drain is prolonged and therefore, the ON resistance is increased. Further, the resistance of a semiconductor layer is generally larger than that of a metal conductor and therefore, in respect of the semiconductor layer 02 meandering as shown by FIG. 5, the high frequency impedance of the meandering portion is increased which gives rise to deterioration of the element.
It is the object of the present invention disclosed in the specification to resolve the above-described problem.